Artichoke Horn

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This is a re-packaging of info from an old horn build - not mine. The original info is scattered across the High Efficiency Speaker Asylum, I'm just piling it into one place. The "Artichoke Horn" was Greg B's speaker at a late 90's Burning Man festival.

I saw a photo of this system years ago, and was quite intrigued. I recently realised that a horn of this scale would be a perfect fit for a shipping container, and would make a nice (giant) outdoor boombox. This got me intrigued all over again.

Dimensional info follows. These lists are direct quotations (apart from my text in brackets), and can be found with a search of the High Efficiency Speaker Asylum:

  • it was a 15' long straight bass horn
  • Think it was about 16-17 ft long including back chamber. I lost the plans.
  • 8x8' mouth
  • it is roughly exponential, or as close as possible given two days of labor and reasonably economical use of standard size plywood
  • it was theoretically a 30hz horn
  • I used ~1:1 compression ratio, including the vent area as part of the driver area
  • throat is ~ 16-17 in sq i think (which would be bigger)
  • Box was 6 cu ft with two 3" radius vents, IIRC

More comments made by the builder (Greg B), on the build / location / setting:

  • it started out as just a folded baffle to control directivity, and then we kind of got carried away
  • Built 4 or 5 years ago when I didn't really know what I was doing. Got lucky or had good instincts (that quotation is from 2003)
  • I have plans somewhere, I'm not quite as subjective as I seem to come across. Unfortunately, I have no idea where they are (so the previous comments were probably partially in jest)
  • Driven by a quite ordinary eminence Kappa15, with Altec horn for HF. Old phase linear 400 powered it. One channel for LF and one for HF
  • We actually were big enough geeks to bring a signal generator and SPL meter to the desert. I was wandering around checking out the festival when my friends were geeking out testing it though. They said audible response into the upper teens, I think the F3 was like 25 or something, but I don't remember really
  • sound quality was great. really loud and low distortion. made the ravers' rows of multiple 4 x 15 cabinets sound like mushy overpriced ghettoblasters
  • we went prepared to block the vents and adjust the comp chamber volume if needed, but it wasn't (from these last 3 points, the vent must have worked well, despite Greg B not being able to sim it)
  • this monster horn most definitely had directional bass. It could barely be heard from the back side
  • if you're going to the trouble of making a -straight- horn, I'd consider crossing it over higher (800?) rather than just using it as a sub. Half the fun is the midrange dynamics/impact
  • Early on [at Burning Man] there were lots of home made flamethrowers and buzzjet go carts, big nasty machines, drive-by Barney shooting range, fire everywhere on the burn night

The sim info is from Hornresp, using a ~1:1 throat and excluding the vent, otherwise driver and dimensions are as given above. I'm happy to patch up any errors or omissions that I am alerted to. Also: if someone can get the venting part to sim well, that'd be good.

Pictured: inputs, and output for the exponential horn.

I also pictured a sim based on two rough changes:

1) a conical approximation I came up with (literally my first attempt - there is no optimisation)
2) rear box reduced from 175 litres to 75 litres

...not to attempt to re-create the exact shape of the original, but to show that even with quite rough and ready changes from the 'perfect' horn, the difference in output is trifling. Even throat size (the confusing part of Greg B's info) is benign - when I tried doubling the throat on the conical horn, Hornresp shows a 1.5dB dip at 65Hz.

So to me, it looks great, particularly for a horn that can be put together in two days, in a desert.

For a similar (temporary / desert) build, the only improvement I can see as worthwhile (time : benefit) would be piling some weight, possibly sandbags, on top.

For a permanent build (shipping container), I'd make a few changes: beefier & heavier materials, I'd lengthen the horn slightly (adding LF extension and LF ripple), and I'd prop the container doors open as mouth extensions (reducing the ripple).

For bass-only use, I'd add a J shaped (90 degree bend) bend at the throat. A quad of opposed drivers would then mount into a separate box that simply dropped onto a throat plate. The driver box would essentially be a 'normal' PPSL enclosure rotated 90 degrees.

Note: am not about to build this. Just appreciative / speculative, at the moment.
 

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I watched the Matterhorn video a few days ago. It is an interesting way to squeeze a lot of bass capability into a relatively compact space, but since it was built to satisfy an odd mix of requirements, it doesn't seem to have much to it that can be applied to a normal budget and application.

If I ever did anything of this sort, it would use about 2% of the Matterhorn's budget: a few drivers and many tons of enclosure, rather than the other way around.
 
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Thanks for the info and the photo! :up:
Interesting build, with it being sort of half a horn against the ground. FWIW, the famous W.E. 15A horn is 15 feet long, but curled up. The mouth is about 1/2 that size I think.

Wonder what it sounded like.
 
1) If you're going to the trouble of making a -straight- horn, I'd consider crossing it over higher (800?) rather than just using it as a sub. Half the fun is the midrange dynamics/impact[/LIST]
2)The sim info is from Hornresp, using a ~1:1 throat and excluding the vent, otherwise driver and dimensions are as given above. I'm happy to patch up any errors or omissions that I am alerted to.
3)Even throat size (the confusing part of Greg B's info) is benign - when I tried doubling the throat on the conical horn, Hornresp shows a 1.5dB dip at 65Hz.
4)So to me, it looks great, particularly for a horn that can be put together in two days, in a desert.
For a similar (temporary / desert) build, the only improvement I can see as worthwhile (time : benefit) would be piling some weight, possibly sandbags, on top.
1) True, but when you run a LF driver near or past Xmax (as we tend to do ;^) )it causes A.M. (amplitude modulation) distortion, which makes vocals sound like they are "gargeling". That said, if you don't push the driver too hard, it can sound fine, but the dispersion upwards of 400 Hz is quite narrow on a long exponential horn as described.
2) If the horn is to be used up to 800 Hz or so, the throat should be narrowed to around 6 inches wide for better dispersion and phase response, or better yet, use a phase plug as shown in the photos below. When building/testing the Kangaroo Horn in the parking lot of a big-box lumber store with a parking lot adjacent to the St.Paul motel I lived at, I asked an interested shopper to participate in an A/B test with or without the phase plug, the better clarity the phase plug provided was obvious to him. This type of phase plug is similar to the ones Dave Gunness designed for the 10" mids in the EV MT systems from the mid 1980s.
3) As usual, lower compression ratios reduce output.
4) Large horns can be built in sections in the relative comfort of one's shop, then assembled on site, either using screws, ratchet straps or clamps. Sand bags or fill to reduce cabinet vibrations works well, but is rather labor intensive.

Back in the 1980's I designed an efficient horn system similar to the one you describe, though smaller. By today's standards that system did not go very low, probably an Fc around 65 Hz. It was built on the Island of Tonga for a pop group The Jets, originally from there, who returned to play a free concert.
Hiring in a system would have been too expensive, as the nearest large sound system was in Australia at the time, so the Jets brought 8) EV 15B and 8)JBL 2460 HF drivers on fiberglass copies of McCaully 482 exponential horns, using two stereo amplifiers for the entire sound system. Total cost of the used drivers, HF horns, and local plywood was under $2000 USD for a system that covered Tonga's outdoor soccer stadium with better sound than the islanders had ever heard.
Greg Huber built the pair of huge 4x15" bass horn cabinets with local carpenters, when they fired them up with pink noise the local kids feared that the island kingdom's volcano was starting to erupt, and ran for cover.
The free concerts went well, filling the stadium many times over during multiple shows over several days, though it ultimately cost the Jets some $250,000 dollars between chartered airplane, import/export tariffs, etc.

Art
 

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Tongans are big people, they deserve big speakers! :)

Thanks for the story, Art.
You are welcome!

The father of the Jets, a very big Tongan who lifted weights equal or greater than his own, was once arrested and handcuffed behind his back for multiple parking violations. I don't think he read English, parking signs and meters were not "on his radar". He said to the police officer "cuffs hurt wrists, take off". The officer replied in the negative, so he broke the cuffs off and handed them to back to him. The officer did not attempt to put another pair back on for his ride in the back seat to the station.

Art
 
Hi hollowboy,

Thanks for bringing this up, I have seen this picture off and on, and wondered about the context.

Did you try to draw the horn from the picture to arrive at the Hornresp data? Are there any other pictures, e.g.: an orthogonal side view?

Either way, looks like someone had fun.

Regards,

P.S.: Hi Art. You sure get around. :)
 
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For a permanent build (shipping container), I'd make a few changes: beefier & heavier materials, I'd lengthen the horn slightly (adding LF extension and LF ripple), and I'd prop the container doors open as mouth extensions (reducing the ripple).
Deceiving.. a standard container has the length and the mouth size so that it won't need to be folded. Folding the horn and using the container walls was cursorily discussed in the other thread but unless (maybe) you cut open the side to use as the mouth and therefore won't need to build the open doors into an extension then this whole thing could be built into a fraction of the volume.
 
1) True, but when you run a LF driver near or past Xmax (as we tend to do ;^) )it causes A.M. (amplitude modulation) distortion, which makes vocals sound like they are "gargeling". That said, if you don't push the driver too hard, it can sound fine, but the dispersion upwards of 400 Hz is quite narrow on a long exponential horn as described.

I haven't heard gargle in years, since I moved up from bookshelf speakers. But yes, I was thinking it would be one of two options-

Like the original: straight throat, large bandwidth, maybe 30-800Hz, ~110dB peaks

As a sub: two or four drivers, J-shape throat, maybe 20-100Hz, ~120dB peaks

Using a modular throat, one could try swapping between these options.

2) If the horn is to be used up to 800 Hz or so, the throat should be narrowed to around 6 inches wide for better dispersion and phase response, or better yet, use a phase plug as shown in the photos below.
Interesting. You mean a slot throat (6' wide, 15' high)?

Your axe-head shaped 'plug' looks like a do-able project (without getting fancy with CNC or casting). Would there be any negative to continuing that division for the first metre (or more) of the throat - like a multicell? I've long been curious about applying the multicell concept to a cone driver.

3) As usual, lower compression ratios reduce output.
Yea, but I was surprised by how little. The shonky model I tried (dodgy expansion, bigger throat, smaller rear chamber) was a 'torture test' to see how an imperfect horn might perform. The deficits of multiple compromises appear negligible - especially compared to the in-room bass variances of normal systems.

The horn as modelled is excursion limited, and excursion is only high at cutoff, so it appears that one could equalise a 1.5dB hole at 65Hz without any harm.

4) Large horns can be built in sections in the relative comfort of one's shop, then assembled on site, either using screws, ratchet straps or clamps. Sand bags or fill to reduce cabinet vibrations works well, but is rather labor intensive.

I had to look up ratchet straps. Cool.

If I ever made a project like this, the shipping container would be the workshop :)

The container would be primarily a tool shed and an anchor point for shade cloth (it gets pretty hot here). I'd cut a door into one side, so I could continue using it for storage; the horn would only use the front 1/3 of a full-sized shipping container.
 
FWIW, the famous W.E. 15A horn is 15 feet long, but curled up. The mouth is about 1/2 that size I think.

I've seen photos of that - but I didn't realise it was so large. I'm glad you mentioned it:

a) simply because it is a beautifully crafted object, IMO, and a good bit of design inspiration.
b) I like how the modules are fitted together. I might steal their idea, one day, e.g. for swappable horn throats.
 
1)I haven't heard gargle in years, since I moved up from bookshelf speakers. But yes, I was thinking it would be one of two options-
Like the original: straight throat, large bandwidth, maybe 30-800Hz, ~110dB peaks
As a sub: two or four drivers, J-shape throat, maybe 20-100Hz, ~120dB peaks
2) Interesting. You mean a slot throat (6' wide, 15' high)?
Your axe-head shaped 'plug' looks like a do-able project (without getting fancy with CNC or casting). Would there be any negative to continuing that division for the first metre (or more) of the throat - like a multicell? I've long been curious about applying the multicell concept to a cone driver.
3)If I ever made a project like this, the shipping container would be the workshop :)
The container would be primarily a tool shed and an anchor point for shade cloth (it gets pretty hot here). I'd cut a door into one side, so I could continue using it for storage; the horn would only use the front 1/3 of a full-sized shipping container.
1) Using a moderate excursion (around 6MM Xmax) single woofer on a huge straight horn covering 30 to 800 Hz could effortlessly (cleanly) do well in excess of 125 dB at one meter. With four drivers in the 20-100 Hz range you could jack that up by an easy 6 dB, and you would not get "dirty" complaints with 140 dB peaks.
2) Yes, you can see how it was made from the pictures, just used a table saw and router. There is no reason to continue the phase plug past the wavelength it is designed to work to. Multicell horns are not a design I would choose for any reason other than the nostalgic "sound" they evoke, which ain't bad, but is a far cry from providing the even polar response I prefer.
3) I built dozens of cabinets in a shop/sound equipment 18' utility trailer (side and rear doors, 4" rear equipment partition), had some really serious wrecks with it due to not reloading to place the primary mass in the center of the trailer before taking off to do gigs. Be careful if you use a full-sized shipping container to move gear if the load is not centered or evenly distributed, or you might end up like I did, having to steer a runaway trailer away from traffic after the class III hitch sheared off when the trailer went into a death shimmy and threw the rear of the tow van into a retaining wall, breaking it loose across three lanes of traffic.

It was scary, and made me late for the load in, had to get the trailer towed back to the motel, replace the bent wheel on the van, and then load the equipment from the trailer in to it.

Then the load in had a flight of stairs, and no stage hands...

I got to get out of my memories of the "good old days.."

Art
 
1) Using a moderate excursion (around 6MM Xmax) single woofer on a huge straight horn covering 30 to 800 Hz could effortlessly (cleanly) do well in excess of 125 dB at one meter. With four drivers in the 20-100 Hz range you could jack that up by an easy 6 dB, and you would not get "dirty" complaints with 140 dB peaks.

I tweaked my Artichoke sim to check that: yep, reducing the box to 50 litres would give 125dB with 6mm excursion (the penalty being a 2dB dip at 40Hz).

I'm way more conservative than you / listen relatively quietly. The one time I had a big (fixed) system, where I could play as loud as I wanted, I still used pretty low power. When I really cranked it (by my standards), the meter indicated I was only using the first couple of watts, of a 70 watt amp.

The LF portion was cheapo 15" drivers, but a quad, and corner loaded, so the system should have been ~100dB per watt.

Based on this, I think I'd only ever use a watt or two if running a big horn rig (107 dB/watt). So a really tiny amp would do it: battery power.

There is no reason to continue the phase plug past the wavelength it is designed to work to.
OK, thanks.

Good (scary!) trailer story - but not for me: if I went down this route, it would be a fixed installation.

That is: if I get a container, it'd be mainly as a shed, for storage & general utility. The horn would be a bonus that I'd only need to buy the concrete for - I have plenty of scrap wood, and various suitable drivers just sitting there.
 
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1)I tweaked my Artichoke sim to check that: yep, reducing the box to 50 litres would give 125dB with 6mm excursion (the penalty being a 2dB dip at 40Hz).
2)I'm way more conservative than you / listen relatively quietly.
Based on this, I think I'd only ever use a watt or two if running a big horn rig (107 dB/watt). So a really tiny amp would do it: battery power.
3)Good (scary!) trailer story - but not for me: if I went down this route, it would be a fixed installation.
Hollowboy,

1) I was just going from my memories of big horn measurements, glad they were correct.
2) I never mix or listen to music at over OSHA prescribed levels even at concerts. At home I seldom exceed 80 dBA, though I don't mind 30-40 Hz at 110 dB now and then.
Even using relatively inefficient speakers, a 15 watt solar panel with a reasonably sized battery would easily power a class D amp for my listening levels even in the shop, keeping up with power tools.
3) What is really scary evidence of my failure to learn from mistakes is that was the second "trailer wagging the van" event. The first time the trailer whipped the van's rear wheel into the freeway curb hard enough to break the wheel off the axle, and the lateral force bent two of the four trailer wheels on the opposite side enough that one tire blew out from rubbing before we made it back to the storage pen after dropping off some speakers loaned to a record store friend of a friend. Hmm, that friend also convinced me to haul a marginally packed over-loaded flat-bed trailer across country too..

Fortunately we were able to get back to tow the three-wheeled van back home just before it was going to be hauled to an impound lot.

At any rate, good to hear your intentions for the container would be static.

Back when I was selling "sound by the pound", and USA trailers had grown bigger and bigger, bought a "small" 40 foot "reefer" (insulated for refrigeration) trailer for just $1500. The 286 square feet of interior space paid for itself in reduced warehouse rental space needed in less than a year, and being truck height, made transferring gear in and out a breeze. I sold the reefer with the rest of my company's gear after using it for 7 more years, it still towed as good as new.

Art
 
Horn:throat & phase plug

... 2) If the horn is to be used up to 800 Hz or so, the throat should be narrowed to around 6 inches wide for better dispersion and phase response, or better yet, use a phase plug as shown in the photos below. ...... This type of phase plug is similar to the ones Dave Gunness designed for the 10" mids in the EV MT systems from the mid 1980s.... Art

Hi there Art: Many thanks for the information on horn throat configuration and/or design of phase plug per photographs. Always wondered why the A7 I constructed from Altec plans, in 1963, had a throat narrowed from 15" driver to 8-inch wide x 16"long slot. ...regards Michael
 
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Hi there Art: Many thanks for the information on horn throat configuration and/or design of phase plug per photographs. Always wondered why the A7 I constructed from Altec plans, in 1963, had a throat narrowed from 15" driver to 8-inch wide x 16"long slot. ...regards Michael
Michael,

1963 build, jeez, you must be a really old fart, I hadn't even heard one before 1969 or so :wchair: :D .

Glad to be "At" attention, and to have explained your "wonders" :hohoho:

Cheers and Happy Black Friday Holidays!

"At"
 
I'm creeping forward on my shipping container idea. I'm still at the stage of clearing the obstacles, figurative and literal:

-I need a building permit ($500 and paperwork)
-Physical access (I'm removing a few trees so a big truck can get in)

I'd like advice on choosing between two layouts:

Layout 1) is basically the horn in post 1, but split for stereo.

Or imagine the attached white picture, crammed into a 8' wide space (no gap between horns).
I would similarly use 4 drivers per side to keep the horn short(ish)
LF horns would be 4m long (flat to 30Hz)
I'd try this as a 3-way, with 4" / 1" horns for HF, permanently nested inside the LF horns

Pros: simple, I like the look, maximal use of the big horn.
Cons: not sure if it will work. Small sweet spot.

Layout 2 ) is basically the post 1 (mono) horn, plus separate mains for stereo. I'd probably use a pair of 18" for the LF horn.

In this case, I'd mount the mains on the inside of the shipping container doors (with castors on the doors, to cope with the additional weight), to make setup as simple as swinging the doors open.

Pros: easier to get right, better use of drivers I already have
Cons: seems like a waste of the big horn.
lower crossovers = bigger c-to-c spacing on mid-HF cross & requiring a 2" tweeter = poorer HF (or need to go 4-way).

So it seems like 1) would be a better nearfield system, 2) would be better further out, with a bigger sweet spot.

Is there something else I haven't thought of, that would rule out either option?

Electronics:

I'd love to keep it simple and use what I already know.

miniDSP as active crossover
Dayton Audio DTA-1 for HF
Trends Audio amp for LF

Can I simply run a mini DSP from a powerbank (a battery with a USB interface, intended for recharging smartphones)?

The DTA-1 is built to run off AA batteries. It sounds thin to me, as a full range amp, but should be OK as a HF amp.

The Trends Audio is a nice amp, mine runs very cool even compared to other amps of the type, and lots of people use it with battery power. Their website says: "The 12V lead-acid rechargeable battery should be a good alternative (battery provides purer DC than electric network)."

I'd use passive components for the mid-high cross.

Have I missed anything obvious with this? I'll transpose this part to an amp forum if that'd be better.

Background / limitations:

  • I'd like to be able to seal it up easily between visits (the doors must remain functional, this sets the horn mouth to a maximum of 244x259cm - 8' wide and 8'6" tall).
  • I will add a secondary door at the other end, so I can use the rest of the container for storage.
  • I want to run it off batteries.
  • My electronics skills are basic. I can solder and use a multimeter, but I know little about power supply.
  • I have a lot of drivers and parts already.
  • I'm in no hurry.
  • Any critical listening will be nearfield and 1 watt will be plenty.
  • I'm not a components snob; a mini DSP sounds fine to me.
  • I'm happy to do all the construction.
  • Weight is no issue - I will build with cheap ply then add a ton or three of concrete.
 

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